The present invention relates generally to measuring a repeat length on a moving web, and more particularly, to such measurements which are made in connection with the printing and assembling of the various parts of a multi-part business form.
Multi-part business forms are common in a wide variety of environments. Such forms comprise multiple parts or layers secured together for use in recording information, typically used to provide multiple copies of the completed form. Such forms are preprinted and commonly include a series of equidistant spaced line holes positioned near each margin of the form, so that the forms can be handled in automated printing equipment and the like. Further, it is typical to provide such forms with various perforations, file holes positioned near the upper edge of each form, sequential numbering of forms, and the like.
When such multi-part forms are manufactured, each part or layer is individually prepared in a specialized press generally known as a forms press. One example of such a press is shown in U.S. Pat. No. 4,512,256. Web material is drawn into the press from a supply roll, and as the web moves through the press, various operations are performed on the web. Such operations can include printing, hole punching, perforating, numbering and the like. As the web emerges from the press, it is rewound onto a take-up or rewind roll.
Once each part has been prepared, the rewind rolls carrying the various parts are loaded into a collator, which draws the part webs into the apparatus, assembles the parts in their multi-layer configuration, and secures the parts together. Since each part is prepared with a series of equidistant line holes near each side edge of the part web, an elongated pin conveyor is provided within the collator for use in assembling the parts. Each individual web is directed onto the pin conveyor as the completed multi-layer stack of the form is built.
It should be clear that to produce the multipart form, each individual part must be of a uniform repeat length, both with respect to the part itself, and with respect to the other parts of the form. Otherwise, the various parts may be misaligned when assembled, or may exhibit buckling within the different layers.
Repeat length of each web is, of course, established as the web moves through the press. Thus, the length must be controlled within the press. However, along the pin conveyor where the parts are assembled, and hence where repeat length becomes critical, the web is typically in a relaxed state with close to zero tension. The repeat length of interest is therefore the relaxed length of the web material as it is taken from the rewind roll into the collator.
Provided that the forms manufacturing environment is properly controlled, no significant change in web length will occur from the time that the web is wound onto the rewind roll in the press to the time that the web is unwound into the collator. Thus, if the relaxed repeat length of the web can be properly controlled within the press, the repeat length will be proper within the collator, where such uniformity becomes important. Techniques are known for adjusting the repeat length of the web as it first enters the press from the supply roll, but one cannot assume that the repeat length will remain uniform as the paper web passes through the press. Repeat length can change during the printing process, in part due to the addition of water (dampening liquid) used in lithographic printing, and this change will be retained within the rewind roll and thus into the collator. However, it is also not sufficient simply to measure the repeat length as the web exits the press and thereby control web movement through the press to regulate repeat length. Because the relaxed repeat length is critical within the collator, measuring the repeat length of the tensioned, moving web is not adequate for ensuring that the various webs will perform properly in the collator.
What is needed, therefore, is a system for determining the relaxed repeat length of the web moving through the web press. This measurement information can be used to control infeed from the supply roll of the web into the press so as to adjust the repeat length. As a result of controlling relaxed repeat length of the web as it exits the press, proper registration among webs comprising a multi-part business form can be achieved in a collator.